The frequency band allocated to a service provider or transmitter.
An electromagnetic wave of frequencies between approximately 20KHz and 3GHz.
RADIUS (Remote Authentication Dial-in User Services)
An authentication and access control server that is used for purposes of authenticating whether a user is allowed access into the corporate resources.
RADSL (Rate-Adaptive DSL)
A symmetrical or asymmetrical transmission medium that has a maximum loop length of 18,000 feet (5.5 kilometers) and is deployed as a single twisted-pair cable. It adapts the data rate dynamically, based on any changes that may be occurring in the line conditions and based on the loop length. With RADSL, the rates can vary widely, from 600Kbps to 7Mbps downstream and from 128Kbps to 1Mbps upstream.
RAM (random-access memory)
A type of computer memory that can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes.
RARP (Reverse Address Resolution Protocol)
The TCP/IP protocol that a diskless machine uses at startup to find its address. The machine broadcasts a request that contains its physical hardware address and a server responds by sending the machine its IP address.
RBOC (regional Bell operating company)
One of several independent telephone companies created from the break-up of AT&T.
RC4 (Rivest Cipher 4)
A streaming cipher technique; a stream cipher adds the output of a pseudorandom number generator bit by bit to the sequential bits of the digitized plain text.
(1) The portion of the total information contained in a message that can be eliminated without loss in essential information. (2) The provision of duplicate, backup equipment to immediately take over the function of equipment that fails. (3) In a database, the storage of the same data item or group of items in two or more files.
An automatic or a programmed check based on the systematic insertion of components or characters used especially for checking purposes.
(1) A repeater used in telegraph applications to retime and retransmit the received signal impulses and restore them to their original strength. These repeaters are speed-and-code sensitive and are intended for use with standard speeds and codes. (2) A repeater used in PCM or digital circuits that detects, retimes, and reconstructs the bits transmitted. (3) A LAN interconnect relay device that copies electrical signals from one LAN to another. Also called a regenerator.
The first unit in the assembly of common control equipment in an automatic exchange. The register receives address information in the form of dial pulses or DTMF signals and stores it for possible conversion or translation.
The measure of a network’s availability. Often measured in terms of the number of nines; for example, “five nines” reliability means that the network is available 99.999% of the time.
Pertains to a computer or device that is connected to another computer or device over a communication line.
Communications with a computer or PBX in one location from a device that is physically removed from the location of the computer.
remote access server
A server that provides network access to remote users, generally via analog POTS lines, or perhaps ISDN connections, including dialup protocols and access control for authentication.
remote access software
Sometimes called remote control software, a program that is a superset of the asynchronous communications software market. It allows a PC to have complete control over another PC at a different site.
remote data concentration
A communications processor that is used for multiplexing data from low-speed lines or terminals onto one or more high-speed lines.
A feature or service in which a service technician can dial into a system and be connected to the system and can be connected to the system processor to run diagnostics and perform system administration.
remote monitoring MIB
The MIB that enables any SNMP management console to extract information from a protocol analyzer running RMON.
(1) In analog transmission, equipment that receives a pulse train, amplifies it, and retimes it for retransmission. (2) In digital transmission, equipment that receives a pulse train, reconstructs it, retimes it, and then amplifies the signal for retransmission. (3) In fiber optics, a device that decodes a low-power light signal, converts it to electrical energy, and then retransmits it via an LED or laser-generating light source, often including, some form of signal amplification.
A company that redistributes the services of another common carrier and retails the services to the public.
A simultaneous data path in the reverse direction over a half-duplex facility. Normally it is used for positive/negative acknowledgments of previously received data blocks.
RF (radio frequency)
A frequency that is much higher than the audio frequencies but below the infrared frequencies; usually, above 20KHz.
(1) A ring-shaped contact of a plug, usually positioned between, but insulated from the tip and sleeve. (2) An audible alerting signal on a telephone line. (3) A network topology in which stations are connected to one another in a closed logical circle, with access to the medium passing sequentially from one station to the next by means of polling from a master station or by passing an access token from one station to another; also called a loop.
A connection on a Token Ring MAU used to tie multiple MAUs into a larger ring.
A connection on a Token Ring MAU used to tie multiple MAUs into larger ring.
Any AC or DC signal transmitted over a line or trunk for the purpose of alerting a party at the distant end of an incoming call. The signal can operate a visual or sound-producing device.
RIP (Routing Information Protocol)
A routing protocol used on TCP/IP networks that distributes the addresses of reachable networks and metrics reflecting the degree of difficulty involved in reaching particular networks form particular locations.
A standard four-wire modular connector used with telephones.
An eight-wire modular connector used with UTP.
RO (receive only)
(1) A printer terminal without a keyboard for data entry. (2) A satellite earth station capable of receiving, but not of transmitting, a signal.
An easily reprogrammable, computer-controlled device that can physically manipulate its surroundings.
rotary dial calling
A system that accepts dialing from conventional rotary dial sets that generate pulses.
A device that connects two LAN segments, which use similar or different architectures, at the OSI network layer, Layer 3. The router determines the most efficient route for passing data through an internet. Those packets that contain a network address different from the originating PC’s address are forwarded onto an adjoining network. Multiprotocol routers can handle this job for two or more protocols simultaneously.
A formula that uses metrics (such as path length, destination, next-hop associations, reliability, delay, bandwidth, load, and communication cost) to determine the best path to the destination.
A protocol that enables routers to communicate with each other. Routing protocols include RIP, IGP, OSPF, EGP, and BGP.
A database that tells the router how to send packets to various destinations.
RPC (remote procedure call)
A system that enables an application programmer to distribute programs between computer systems interconnected with a network. RPC development tools eliminate the need for in depth knowledge of diverse network protocols and computing platforms, enabling a programmer to concentrate on developing the application itself.
A technical specification published by the EIA that establishes mechanical and electrical interface requirements between DTE and DCE, employing serial binary data interchange and operating at speeds up to 19.2Kbps.
An EIA standard for interfaces between DTE and automatic calling equipment for data communication.
An EIA specification for electrical characteristics of balanced voltage digital interface circuits.
An EIA specification for electrical characteristics of unbalanced-voltage digital interface circuits.
An EIA specification for general-purpose, 37-position and 9-position interface for DTE and DCE, employing serial binary data interchange and operating at speeds up to 2Mbps.
RSA (Rivest, Shamir, and Adelman)
A public key algorithm whose security derives from the difficulty of factoring large prime integers.
RSVP (Reservation Resource Protocol)
A protocol that enables an internet to support specified levels of QoS. By using RSVP, an application is capable of reserving resources along a route from source to destination. RSVP-enabled routers then schedule and prioritize packets to fulfill the QoS.
RTCP (Real-Time Control Protocol)
An ITU protocol that provides status feedback from senders to receivers.
RTP (Real-Time Transport Protocol)
An Internet protocol for transmitting real-time data such as audio and video. RTP itself does not guarantee real-time delivery of data, but it does provide mechanisms for the sending and receiving applications to support streaming data.
RTSP (Real-Time Streaming Protocol)
A protocol that runs on top of IP multicasting, UDP, RTP, and RTCP.